treewide: use Fatal in tests instead of Error

Error doesn't return the goroutine, but these cases are final and should end the test case.

Change-Id: I9d87e268b56acd7d1ff5883bb82bf3d74c309176
Reviewed-on: https://review.monogon.dev/c/monogon/+/4044
Reviewed-by: Jan Schär <jan@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/bringup/test/run_test.go b/osbase/bringup/test/run_test.go
index 70003cb..085b875 100644
--- a/osbase/bringup/test/run_test.go
+++ b/osbase/bringup/test/run_test.go
@@ -69,7 +69,7 @@
 	expectedOutput := "_BRINGUP_LAUNCH_SUCCESS_"
 	result, err := runQemu(ctx, extraArgs, expectedOutput)
 	if err != nil {
-		t.Error(err.Error())
+		t.Error(err)
 	}
 	if !result {
 		t.Errorf("QEMU didn't produce the expected output %q", expectedOutput)
@@ -85,7 +85,7 @@
 	expectedOutput := "root runnable paniced"
 	result, err := runQemu(ctx, extraArgs, expectedOutput)
 	if err != nil {
-		t.Error(err.Error())
+		t.Error(err)
 	}
 	if !result {
 		t.Errorf("QEMU didn't produce the expected output %q", expectedOutput)
@@ -102,7 +102,7 @@
 	expectedOutput := "this is an error"
 	result, err := runQemu(ctx, extraArgs, expectedOutput)
 	if err != nil {
-		t.Error(err.Error())
+		t.Error(err)
 	}
 	if !result {
 		t.Errorf("QEMU didn't produce the expected output %q", expectedOutput)